These steps should work to compile the 49c version:
1) download and install speech api (only if it is not installed yet)
2) download and install WMFSDK9 (only if it is not installed yet) and put in options - projects - vc++ directories "C:\Programmi\WMSDK\WMFSDK9\include" (under "Include Files"), and "C:\Programmi\WMSDK\WMFSDK9\lib" under "Library Files"
3) download and unpack emule0.49c- sources
4) download and unpack the eMule 0.49b libs archive: ed2k://|file|eMule-0.49b-libs.zip|1732292|0D1C22554DD88A11883D73B3624D929D|/
5) copy-paste only the folders crypto51, libpng, resizablelib (not the zlib folder !!!) --> in the 49c-sources folder ...
6) at this point, build only the resizablelib and then rename the release folder in ReleaseUnicode
7) build the emule_vc71-all.sln

I even have modified the code as you suggested...(Although I am not sure in which way that could could be relevant to this problem, )

well, it should work without my modifications, since i only didn't want to see those warnings and i tried to eliminate them; and you should know that i'm not a programmer, so they are not relevant..
anyway it seems you have already done

5) delete the zlib and libpng folders in the 0.50a sources (i have gotten and included in the 0.50a libs archive the zlib_vc71.sln and .vcproj from the zlib folder of 0.50a sources) and copy all the directories of 0.50a libs near the 0.50a folders:

[OR extract and open the folder 0.49b libs, open the zlib folder, delete emule_vc71.sln and emule_vc71.vcproj, then copy-paste all the folders (crypto51, libpng 1.4.1 needed, resizablelib, zlib) in the 0.50a-sources folder]

6) open the emule_vc71-all.sln in the srchybrid folder and build the emule_vc71-all.sln in release mode

Anyway emule is compiled in this way... Is it correct or did I make some damage?
...

Hey xilolee, if you were using the libpng 1.4.1 from the libpng site, I noticed that the actual project file has some incorrect settings: The static libraries are set to compile as multi-threaded dll's, NOT lib's, so you have to set the Debug and and Release options manually to build static lib's. This is why you get the import error when the functions/etc are meant to be exported.

After setting the linker options it should build without those warnings.